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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.net;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Random;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.ArrayList;
import java.util.ServiceLoader;
import java.security.AccessController;
import java.io.ObjectStreamException;
import java.io.ObjectStreamField;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectInputStream.GetField;
import java.io.ObjectOutputStream;
import java.io.ObjectOutputStream.PutField;
import sun.security.action.*;
import sun.net.InetAddressCachePolicy;
import sun.net.util.IPAddressUtil;
import sun.net.spi.nameservice.*;

/**
 * This class represents an Internet Protocol (IP) address.
 *
 * <p> An IP address is either a 32-bit or 128-bit unsigned number
 * used by IP, a lower-level protocol on which protocols like UDP and
 * TCP are built. The IP address architecture is defined by <a
 * href="http://www.ietf.org/rfc/rfc790.txt"><i>RFC&nbsp;790:
 * Assigned Numbers</i></a>, <a
 * href="http://www.ietf.org/rfc/rfc1918.txt"> <i>RFC&nbsp;1918:
 * Address Allocation for Private Internets</i></a>, <a
 * href="http://www.ietf.org/rfc/rfc2365.txt"><i>RFC&nbsp;2365:
 * Administratively Scoped IP Multicast</i></a>, and <a
 * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IP
 * Version 6 Addressing Architecture</i></a>. An instance of an
 * InetAddress consists of an IP address and possibly its
 * corresponding host name (depending on whether it is constructed
 * with a host name or whether it has already done reverse host name
 * resolution).
 *
 * <h3> Address types </h3>
 *
 * <blockquote><table cellspacing=2 summary="Description of unicast and multicast address types">
 * <tr><th valign=top><i>unicast</i></th>
 * <td>An identifier for a single interface. A packet sent to
 * a unicast address is delivered to the interface identified by
 * that address.
 *
 * <p> The Unspecified Address -- Also called anylocal or wildcard
 * address. It must never be assigned to any node. It indicates the
 * absence of an address. One example of its use is as the target of
 * bind, which allows a server to accept a client connection on any
 * interface, in case the server host has multiple interfaces.
 *
 * <p> The <i>unspecified</i> address must not be used as
 * the destination address of an IP packet.
 *
 * <p> The <i>Loopback</i> Addresses -- This is the address
 * assigned to the loopback interface. Anything sent to this
 * IP address loops around and becomes IP input on the local
 * host. This address is often used when testing a
 * client.</td></tr>
 * <tr><th valign=top><i>multicast</i></th>
 * <td>An identifier for a set of interfaces (typically belonging
 * to different nodes). A packet sent to a multicast address is
 * delivered to all interfaces identified by that address.</td></tr>
 * </table></blockquote>
 *
 * <h4> IP address scope </h4>
 *
 * <p> <i>Link-local</i> addresses are designed to be used for addressing
 * on a single link for purposes such as auto-address configuration,
 * neighbor discovery, or when no routers are present.
 *
 * <p> <i>Site-local</i> addresses are designed to be used for addressing
 * inside of a site without the need for a global prefix.
 *
 * <p> <i>Global</i> addresses are unique across the internet.
 *
 * <h4> Textual representation of IP addresses </h4>
 *
 * The textual representation of an IP address is address family specific.
 *
 * <p>
 *
 * For IPv4 address format, please refer to <A
 * HREF="Inet4Address.html#format">Inet4Address#format</A>; For IPv6
 * address format, please refer to <A
 * HREF="Inet6Address.html#format">Inet6Address#format</A>.
 *
 * <P>There is a <a href="doc-files/net-properties.html#Ipv4IPv6">couple of
 * System Properties</a> affecting how IPv4 and IPv6 addresses are used.</P>
 *
 * <h4> Host Name Resolution </h4>
 *
 * Host name-to-IP address <i>resolution</i> is accomplished through
 * the use of a combination of local machine configuration information
 * and network naming services such as the Domain Name System (DNS)
 * and Network Information Service(NIS). The particular naming
 * services(s) being used is by default the local machine configured
 * one. For any host name, its corresponding IP address is returned.
 *
 * <p> <i>Reverse name resolution</i> means that for any IP address,
 * the host associated with the IP address is returned.
 *
 * <p> The InetAddress class provides methods to resolve host names to
 * their IP addresses and vice versa.
 *
 * <h4> InetAddress Caching </h4>
 *
 * The InetAddress class has a cache to store successful as well as
 * unsuccessful host name resolutions.
 *
 * <p> By default, when a security manager is installed, in order to
 * protect against DNS spoofing attacks,
 * the result of positive host name resolutions are
 * cached forever. When a security manager is not installed, the default
 * behavior is to cache entries for a finite (implementation dependent)
 * period of time. The result of unsuccessful host
 * name resolution is cached for a very short period of time (10
 * seconds) to improve performance.
 *
 * <p> If the default behavior is not desired, then a Java security property
 * can be set to a different Time-to-live (TTL) value for positive
 * caching. Likewise, a system admin can configure a different
 * negative caching TTL value when needed.
 *
 * <p> Two Java security properties control the TTL values used for
 * positive and negative host name resolution caching:
 *
 * <blockquote>
 * <dl>
 * <dt><b>networkaddress.cache.ttl</b></dt>
 * <dd>Indicates the caching policy for successful name lookups from
 * the name service. The value is specified as as integer to indicate
 * the number of seconds to cache the successful lookup. The default
 * setting is to cache for an implementation specific period of time.
 * <p>
 * A value of -1 indicates "cache forever".
 * </dd>
 * <dt><b>networkaddress.cache.negative.ttl</b> (default: 10)</dt>
 * <dd>Indicates the caching policy for un-successful name lookups
 * from the name service. The value is specified as as integer to
 * indicate the number of seconds to cache the failure for
 * un-successful lookups.
 * <p>
 * A value of 0 indicates "never cache".
 * A value of -1 indicates "cache forever".
 * </dd>
 * </dl>
 * </blockquote>
 *
 * @author Chris Warth
 * @see java.net.InetAddress#getByAddress(byte[])
 * @see java.net.InetAddress#getByAddress(java.lang.String, byte[])
 * @see java.net.InetAddress#getAllByName(java.lang.String)
 * @see java.net.InetAddress#getByName(java.lang.String)
 * @see java.net.InetAddress#getLocalHost()
 * @since JDK1.0
 */
public class InetAddress implements java.io.Serializable {

  /**
   * Specify the address family: Internet Protocol, Version 4
   *
   * @since 1.4
   */
  static final int IPv4 = 1;

  /**
   * Specify the address family: Internet Protocol, Version 6
   *
   * @since 1.4
   */
  static final int IPv6 = 2;

  /* Specify address family preference */
  static transient boolean preferIPv6Address = false;

  static class InetAddressHolder {

    /**
     * Reserve the original application specified hostname.
     *
     * The original hostname is useful for domain-based endpoint
     * identification (see RFC 2818 and RFC 6125).  If an address
     * was created with a raw IP address, a reverse name lookup
     * may introduce endpoint identification security issue via
     * DNS forging.
     *
     * Oracle JSSE provider is using this original hostname, via
     * sun.misc.JavaNetAccess, for SSL/TLS endpoint identification.
     *
     * Note: May define a new public method in the future if necessary.
     */
    private String originalHostName;

    InetAddressHolder() {
    }

    InetAddressHolder(String hostName, int address, int family) {
      this.originalHostName = hostName;
      this.hostName = hostName;
      this.address = address;
      this.family = family;
    }

    void init(String hostName, int family) {
      this.originalHostName = hostName;
      this.hostName = hostName;
      if (family != -1) {
        this.family = family;
      }
    }

    String hostName;

    String getHostName() {
      return hostName;
    }

    String getOriginalHostName() {
      return originalHostName;
    }

    /**
     * Holds a 32-bit IPv4 address.
     */
    int address;

    int getAddress() {
      return address;
    }

    /**
     * Specifies the address family type, for instance, '1' for IPv4
     * addresses, and '2' for IPv6 addresses.
     */
    int family;

    int getFamily() {
      return family;
    }
  }

  /* Used to store the serializable fields of InetAddress */
  final transient InetAddressHolder holder;

  InetAddressHolder holder() {
    return holder;
  }

  /* Used to store the name service provider */
  private static List<NameService> nameServices = null;

  /* Used to store the best available hostname */
  private transient String canonicalHostName = null;

  /**
   * use serialVersionUID from JDK 1.0.2 for interoperability
   */
  private static final long serialVersionUID = 3286316764910316507L;

  /*
   * Load net library into runtime, and perform initializations.
   */
  static {
    preferIPv6Address = java.security.AccessController.doPrivileged(
        new GetBooleanAction("java.net.preferIPv6Addresses")).booleanValue();
    AccessController.doPrivileged(
        new java.security.PrivilegedAction<Void>() {
          public Void run() {
            System.loadLibrary("net");
            return null;
          }
        });
    init();
  }

  /**
   * Constructor for the Socket.accept() method.
   * This creates an empty InetAddress, which is filled in by
   * the accept() method.  This InetAddress, however, is not
   * put in the address cache, since it is not created by name.
   */
  InetAddress() {
    holder = new InetAddressHolder();
  }

  /**
   * Replaces the de-serialized object with an Inet4Address object.
   *
   * @return the alternate object to the de-serialized object.
   * @throws ObjectStreamException if a new object replacing this object could not be created
   */
  private Object readResolve() throws ObjectStreamException {
    // will replace the deserialized 'this' object
    return new Inet4Address(holder().getHostName(), holder().getAddress());
  }

  /**
   * Utility routine to check if the InetAddress is an
   * IP multicast address.
   *
   * @return a {@code boolean} indicating if the InetAddress is an IP multicast address
   * @since JDK1.1
   */
  public boolean isMulticastAddress() {
    return false;
  }

  /**
   * Utility routine to check if the InetAddress in a wildcard address.
   *
   * @return a {@code boolean} indicating if the Inetaddress is a wildcard address.
   * @since 1.4
   */
  public boolean isAnyLocalAddress() {
    return false;
  }

  /**
   * Utility routine to check if the InetAddress is a loopback address.
   *
   * @return a {@code boolean} indicating if the InetAddress is a loopback address; or false
   * otherwise.
   * @since 1.4
   */
  public boolean isLoopbackAddress() {
    return false;
  }

  /**
   * Utility routine to check if the InetAddress is an link local address.
   *
   * @return a {@code boolean} indicating if the InetAddress is a link local address; or false if
   * address is not a link local unicast address.
   * @since 1.4
   */
  public boolean isLinkLocalAddress() {
    return false;
  }

  /**
   * Utility routine to check if the InetAddress is a site local address.
   *
   * @return a {@code boolean} indicating if the InetAddress is a site local address; or false if
   * address is not a site local unicast address.
   * @since 1.4
   */
  public boolean isSiteLocalAddress() {
    return false;
  }

  /**
   * Utility routine to check if the multicast address has global scope.
   *
   * @return a {@code boolean} indicating if the address has is a multicast address of global scope,
   * false if it is not of global scope or it is not a multicast address
   * @since 1.4
   */
  public boolean isMCGlobal() {
    return false;
  }

  /**
   * Utility routine to check if the multicast address has node scope.
   *
   * @return a {@code boolean} indicating if the address has is a multicast address of node-local
   * scope, false if it is not of node-local scope or it is not a multicast address
   * @since 1.4
   */
  public boolean isMCNodeLocal() {
    return false;
  }

  /**
   * Utility routine to check if the multicast address has link scope.
   *
   * @return a {@code boolean} indicating if the address has is a multicast address of link-local
   * scope, false if it is not of link-local scope or it is not a multicast address
   * @since 1.4
   */
  public boolean isMCLinkLocal() {
    return false;
  }

  /**
   * Utility routine to check if the multicast address has site scope.
   *
   * @return a {@code boolean} indicating if the address has is a multicast address of site-local
   * scope, false if it is not of site-local scope or it is not a multicast address
   * @since 1.4
   */
  public boolean isMCSiteLocal() {
    return false;
  }

  /**
   * Utility routine to check if the multicast address has organization scope.
   *
   * @return a {@code boolean} indicating if the address has is a multicast address of
   * organization-local scope, false if it is not of organization-local scope or it is not a
   * multicast address
   * @since 1.4
   */
  public boolean isMCOrgLocal() {
    return false;
  }


  /**
   * Test whether that address is reachable. Best effort is made by the
   * implementation to try to reach the host, but firewalls and server
   * configuration may block requests resulting in a unreachable status
   * while some specific ports may be accessible.
   * A typical implementation will use ICMP ECHO REQUESTs if the
   * privilege can be obtained, otherwise it will try to establish
   * a TCP connection on port 7 (Echo) of the destination host.
   * <p>
   * The timeout value, in milliseconds, indicates the maximum amount of time
   * the try should take. If the operation times out before getting an
   * answer, the host is deemed unreachable. A negative value will result
   * in an IllegalArgumentException being thrown.
   *
   * @param timeout the time, in milliseconds, before the call aborts
   * @return a {@code boolean} indicating if the address is reachable.
   * @throws IOException if a network error occurs
   * @throws IllegalArgumentException if {@code timeout} is negative.
   * @since 1.5
   */
  public boolean isReachable(int timeout) throws IOException {
    return isReachable(null, 0, timeout);
  }

  /**
   * Test whether that address is reachable. Best effort is made by the
   * implementation to try to reach the host, but firewalls and server
   * configuration may block requests resulting in a unreachable status
   * while some specific ports may be accessible.
   * A typical implementation will use ICMP ECHO REQUESTs if the
   * privilege can be obtained, otherwise it will try to establish
   * a TCP connection on port 7 (Echo) of the destination host.
   * <p>
   * The {@code network interface} and {@code ttl} parameters
   * let the caller specify which network interface the test will go through
   * and the maximum number of hops the packets should go through.
   * A negative value for the {@code ttl} will result in an
   * IllegalArgumentException being thrown.
   * <p>
   * The timeout value, in milliseconds, indicates the maximum amount of time
   * the try should take. If the operation times out before getting an
   * answer, the host is deemed unreachable. A negative value will result
   * in an IllegalArgumentException being thrown.
   *
   * @param netif the NetworkInterface through which the test will be done, or null for any
   * interface
   * @param ttl the maximum numbers of hops to try or 0 for the default
   * @param timeout the time, in milliseconds, before the call aborts
   * @return a {@code boolean}indicating if the address is reachable.
   * @throws IllegalArgumentException if either {@code timeout} or {@code ttl} are negative.
   * @throws IOException if a network error occurs
   * @since 1.5
   */
  public boolean isReachable(NetworkInterface netif, int ttl,
      int timeout) throws IOException {
    if (ttl < 0) {
      throw new IllegalArgumentException("ttl can't be negative");
    }
    if (timeout < 0) {
      throw new IllegalArgumentException("timeout can't be negative");
    }

    return impl.isReachable(this, timeout, netif, ttl);
  }

  /**
   * Gets the host name for this IP address.
   *
   * <p>If this InetAddress was created with a host name,
   * this host name will be remembered and returned;
   * otherwise, a reverse name lookup will be performed
   * and the result will be returned based on the system
   * configured name lookup service. If a lookup of the name service
   * is required, call
   * {@link #getCanonicalHostName() getCanonicalHostName}.
   *
   * <p>If there is a security manager, its
   * {@code checkConnect} method is first called
   * with the hostname and {@code -1}
   * as its arguments to see if the operation is allowed.
   * If the operation is not allowed, it will return
   * the textual representation of the IP address.
   *
   * @return the host name for this IP address, or if the operation is not allowed by the security
   * check, the textual representation of the IP address.
   * @see InetAddress#getCanonicalHostName
   * @see SecurityManager#checkConnect
   */
  public String getHostName() {
    return getHostName(true);
  }

  /**
   * Returns the hostname for this address.
   * If the host is equal to null, then this address refers to any
   * of the local machine's available network addresses.
   * this is package private so SocketPermission can make calls into
   * here without a security check.
   *
   * <p>If there is a security manager, this method first
   * calls its {@code checkConnect} method
   * with the hostname and {@code -1}
   * as its arguments to see if the calling code is allowed to know
   * the hostname for this IP address, i.e., to connect to the host.
   * If the operation is not allowed, it will return
   * the textual representation of the IP address.
   *
   * @param check make security check if true
   * @return the host name for this IP address, or if the operation is not allowed by the security
   * check, the textual representation of the IP address.
   * @see SecurityManager#checkConnect
   */
  String getHostName(boolean check) {
    if (holder().getHostName() == null) {
      holder().hostName = InetAddress.getHostFromNameService(this, check);
    }
    return holder().getHostName();
  }

  /**
   * Gets the fully qualified domain name for this IP address.
   * Best effort method, meaning we may not be able to return
   * the FQDN depending on the underlying system configuration.
   *
   * <p>If there is a security manager, this method first
   * calls its {@code checkConnect} method
   * with the hostname and {@code -1}
   * as its arguments to see if the calling code is allowed to know
   * the hostname for this IP address, i.e., to connect to the host.
   * If the operation is not allowed, it will return
   * the textual representation of the IP address.
   *
   * @return the fully qualified domain name for this IP address, or if the operation is not allowed
   * by the security check, the textual representation of the IP address.
   * @see SecurityManager#checkConnect
   * @since 1.4
   */
  public String getCanonicalHostName() {
    if (canonicalHostName == null) {
      canonicalHostName =
          InetAddress.getHostFromNameService(this, true);
    }
    return canonicalHostName;
  }

  /**
   * Returns the hostname for this address.
   *
   * <p>If there is a security manager, this method first
   * calls its {@code checkConnect} method
   * with the hostname and {@code -1}
   * as its arguments to see if the calling code is allowed to know
   * the hostname for this IP address, i.e., to connect to the host.
   * If the operation is not allowed, it will return
   * the textual representation of the IP address.
   *
   * @param check make security check if true
   * @return the host name for this IP address, or if the operation is not allowed by the security
   * check, the textual representation of the IP address.
   * @see SecurityManager#checkConnect
   */
  private static String getHostFromNameService(InetAddress addr, boolean check) {
    String host = null;
    for (NameService nameService : nameServices) {
      try {
        // first lookup the hostname
        host = nameService.getHostByAddr(addr.getAddress());

                /* check to see if calling code is allowed to know
                 * the hostname for this IP address, ie, connect to the host
                 */
        if (check) {
          SecurityManager sec = System.getSecurityManager();
          if (sec != null) {
            sec.checkConnect(host, -1);
          }
        }

                /* now get all the IP addresses for this hostname,
                 * and make sure one of them matches the original IP
                 * address. We do this to try and prevent spoofing.
                 */

        InetAddress[] arr = InetAddress.getAllByName0(host, check);
        boolean ok = false;

        if (arr != null) {
          for (int i = 0; !ok && i < arr.length; i++) {
            ok = addr.equals(arr[i]);
          }
        }

        //XXX: if it looks a spoof just return the address?
        if (!ok) {
          host = addr.getHostAddress();
          return host;
        }

        break;

      } catch (SecurityException e) {
        host = addr.getHostAddress();
        break;
      } catch (UnknownHostException e) {
        host = addr.getHostAddress();
        // let next provider resolve the hostname
      }
    }

    return host;
  }

  /**
   * Returns the raw IP address of this {@code InetAddress}
   * object. The result is in network byte order: the highest order
   * byte of the address is in {@code getAddress()[0]}.
   *
   * @return the raw IP address of this object.
   */
  public byte[] getAddress() {
    return null;
  }

  /**
   * Returns the IP address string in textual presentation.
   *
   * @return the raw IP address in a string format.
   * @since JDK1.0.2
   */
  public String getHostAddress() {
    return null;
  }

  /**
   * Returns a hashcode for this IP address.
   *
   * @return a hash code value for this IP address.
   */
  public int hashCode() {
    return -1;
  }

  /**
   * Compares this object against the specified object.
   * The result is {@code true} if and only if the argument is
   * not {@code null} and it represents the same IP address as
   * this object.
   * <p>
   * Two instances of {@code InetAddress} represent the same IP
   * address if the length of the byte arrays returned by
   * {@code getAddress} is the same for both, and each of the
   * array components is the same for the byte arrays.
   *
   * @param obj the object to compare against.
   * @return {@code true} if the objects are the same; {@code false} otherwise.
   * @see java.net.InetAddress#getAddress()
   */
  public boolean equals(Object obj) {
    return false;
  }

  /**
   * Converts this IP address to a {@code String}. The
   * string returned is of the form: hostname / literal IP
   * address.
   *
   * If the host name is unresolved, no reverse name service lookup
   * is performed. The hostname part will be represented by an empty string.
   *
   * @return a string representation of this IP address.
   */
  public String toString() {
    String hostName = holder().getHostName();
    return ((hostName != null) ? hostName : "")
        + "/" + getHostAddress();
  }

  /*
   * Cached addresses - our own litle nis, not!
   */
  private static Cache addressCache = new Cache(Cache.Type.Positive);

  private static Cache negativeCache = new Cache(Cache.Type.Negative);

  private static boolean addressCacheInit = false;

  static InetAddress[] unknown_array; // put THIS in cache

  static InetAddressImpl impl;

  private static final HashMap<String, Void> lookupTable = new HashMap<>();

  /**
   * Represents a cache entry
   */
  static final class CacheEntry {

    CacheEntry(InetAddress[] addresses, long expiration) {
      this.addresses = addresses;
      this.expiration = expiration;
    }

    InetAddress[] addresses;
    long expiration;
  }

  /**
   * A cache that manages entries based on a policy specified
   * at creation time.
   */
  static final class Cache {

    private LinkedHashMap<String, CacheEntry> cache;
    private Type type;

    enum Type {Positive, Negative}

    ;

    /**
     * Create cache
     */
    public Cache(Type type) {
      this.type = type;
      cache = new LinkedHashMap<String, CacheEntry>();
    }

    private int getPolicy() {
      if (type == Type.Positive) {
        return InetAddressCachePolicy.get();
      } else {
        return InetAddressCachePolicy.getNegative();
      }
    }

    /**
     * Add an entry to the cache. If there's already an
     * entry then for this host then the entry will be
     * replaced.
     */
    public Cache put(String host, InetAddress[] addresses) {
      int policy = getPolicy();
      if (policy == InetAddressCachePolicy.NEVER) {
        return this;
      }

      // purge any expired entries

      if (policy != InetAddressCachePolicy.FOREVER) {

        // As we iterate in insertion order we can
        // terminate when a non-expired entry is found.
        LinkedList<String> expired = new LinkedList<>();
        long now = System.currentTimeMillis();
        for (String key : cache.keySet()) {
          CacheEntry entry = cache.get(key);

          if (entry.expiration >= 0 && entry.expiration < now) {
            expired.add(key);
          } else {
            break;
          }
        }

        for (String key : expired) {
          cache.remove(key);
        }
      }

      // create new entry and add it to the cache
      // -- as a HashMap replaces existing entries we
      //    don't need to explicitly check if there is
      //    already an entry for this host.
      long expiration;
      if (policy == InetAddressCachePolicy.FOREVER) {
        expiration = -1;
      } else {
        expiration = System.currentTimeMillis() + (policy * 1000);
      }
      CacheEntry entry = new CacheEntry(addresses, expiration);
      cache.put(host, entry);
      return this;
    }

    /**
     * Query the cache for the specific host. If found then
     * return its CacheEntry, or null if not found.
     */
    public CacheEntry get(String host) {
      int policy = getPolicy();
      if (policy == InetAddressCachePolicy.NEVER) {
        return null;
      }
      CacheEntry entry = cache.get(host);

      // check if entry has expired
      if (entry != null && policy != InetAddressCachePolicy.FOREVER) {
        if (entry.expiration >= 0 &&
            entry.expiration < System.currentTimeMillis()) {
          cache.remove(host);
          entry = null;
        }
      }

      return entry;
    }
  }

  /*
   * Initialize cache and insert anyLocalAddress into the
   * unknown array with no expiry.
   */
  private static void cacheInitIfNeeded() {
    assert Thread.holdsLock(addressCache);
    if (addressCacheInit) {
      return;
    }
    unknown_array = new InetAddress[1];
    unknown_array[0] = impl.anyLocalAddress();

    addressCache.put(impl.anyLocalAddress().getHostName(),
        unknown_array);

    addressCacheInit = true;
  }

  /*
   * Cache the given hostname and addresses.
   */
  private static void cacheAddresses(String hostname,
      InetAddress[] addresses,
      boolean success) {
    hostname = hostname.toLowerCase();
    synchronized (addressCache) {
      cacheInitIfNeeded();
      if (success) {
        addressCache.put(hostname, addresses);
      } else {
        negativeCache.put(hostname, addresses);
      }
    }
  }

  /*
   * Lookup hostname in cache (positive & negative cache). If
   * found return addresses, null if not found.
   */
  private static InetAddress[] getCachedAddresses(String hostname) {
    hostname = hostname.toLowerCase();

    // search both positive & negative caches

    synchronized (addressCache) {
      cacheInitIfNeeded();

      CacheEntry entry = addressCache.get(hostname);
      if (entry == null) {
        entry = negativeCache.get(hostname);
      }

      if (entry != null) {
        return entry.addresses;
      }
    }

    // not found
    return null;
  }

  private static NameService createNSProvider(String provider) {
    if (provider == null) {
      return null;
    }

    NameService nameService = null;
    if (provider.equals("default")) {
      // initialize the default name service
      nameService = new NameService() {
        public InetAddress[] lookupAllHostAddr(String host)
            throws UnknownHostException {
          return impl.lookupAllHostAddr(host);
        }

        public String getHostByAddr(byte[] addr)
            throws UnknownHostException {
          return impl.getHostByAddr(addr);
        }
      };
    } else {
      final String providerName = provider;
      try {
        nameService = java.security.AccessController.doPrivileged(
            new java.security.PrivilegedExceptionAction<NameService>() {
              public NameService run() {
                Iterator<NameServiceDescriptor> itr =
                    ServiceLoader.load(NameServiceDescriptor.class)
                        .iterator();
                while (itr.hasNext()) {
                  NameServiceDescriptor nsd = itr.next();
                  if (providerName.
                      equalsIgnoreCase(nsd.getType() + ","
                          + nsd.getProviderName())) {
                    try {
                      return nsd.createNameService();
                    } catch (Exception e) {
                      e.printStackTrace();
                      System.err.println(
                          "Cannot create name service:"
                              + providerName + ": " + e);
                    }
                  }
                }

                return null;
              }
            }
        );
      } catch (java.security.PrivilegedActionException e) {
      }
    }

    return nameService;
  }

  static {
    // create the impl
    impl = InetAddressImplFactory.create();

    // get name service if provided and requested
    String provider = null;
    ;
    String propPrefix = "sun.net.spi.nameservice.provider.";
    int n = 1;
    nameServices = new ArrayList<NameService>();
    provider = AccessController.doPrivileged(
        new GetPropertyAction(propPrefix + n));
    while (provider != null) {
      NameService ns = createNSProvider(provider);
      if (ns != null) {
        nameServices.add(ns);
      }

      n++;
      provider = AccessController.doPrivileged(
          new GetPropertyAction(propPrefix + n));
    }

    // if not designate any name services provider,
    // create a default one
    if (nameServices.size() == 0) {
      NameService ns = createNSProvider("default");
      nameServices.add(ns);
    }
  }

  /**
   * Creates an InetAddress based on the provided host name and IP address.
   * No name service is checked for the validity of the address.
   *
   * <p> The host name can either be a machine name, such as
   * "{@code java.sun.com}", or a textual representation of its IP
   * address.
   * <p> No validity checking is done on the host name either.
   *
   * <p> If addr specifies an IPv4 address an instance of Inet4Address
   * will be returned; otherwise, an instance of Inet6Address
   * will be returned.
   *
   * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array
   * must be 16 bytes long
   *
   * @param host the specified host
   * @param addr the raw IP address in network byte order
   * @return an InetAddress object created from the raw IP address.
   * @throws UnknownHostException if IP address is of illegal length
   * @since 1.4
   */
  public static InetAddress getByAddress(String host, byte[] addr)
      throws UnknownHostException {
    if (host != null && host.length() > 0 && host.charAt(0) == '[') {
      if (host.charAt(host.length() - 1) == ']') {
        host = host.substring(1, host.length() - 1);
      }
    }
    if (addr != null) {
      if (addr.length == Inet4Address.INADDRSZ) {
        return new Inet4Address(host, addr);
      } else if (addr.length == Inet6Address.INADDRSZ) {
        byte[] newAddr
            = IPAddressUtil.convertFromIPv4MappedAddress(addr);
        if (newAddr != null) {
          return new Inet4Address(host, newAddr);
        } else {
          return new Inet6Address(host, addr);
        }
      }
    }
    throw new UnknownHostException("addr is of illegal length");
  }


  /**
   * Determines the IP address of a host, given the host's name.
   *
   * <p> The host name can either be a machine name, such as
   * "{@code java.sun.com}", or a textual representation of its
   * IP address. If a literal IP address is supplied, only the
   * validity of the address format is checked.
   *
   * <p> For {@code host} specified in literal IPv6 address,
   * either the form defined in RFC 2732 or the literal IPv6 address
   * format defined in RFC 2373 is accepted. IPv6 scoped addresses are also
   * supported. See <a href="Inet6Address.html#scoped">here</a> for a description of IPv6
   * scoped addresses.
   *
   * <p> If the host is {@code null} then an {@code InetAddress}
   * representing an address of the loopback interface is returned.
   * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
   * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
   * section&nbsp;2.5.3. </p>
   *
   * @param host the specified host, or {@code null}.
   * @return an IP address for the given host name.
   * @throws UnknownHostException if no IP address for the {@code host} could be found, or if a
   * scope_id was specified for a global IPv6 address.
   * @throws SecurityException if a security manager exists and its checkConnect method doesn't
   * allow the operation
   */
  public static InetAddress getByName(String host)
      throws UnknownHostException {
    return InetAddress.getAllByName(host)[0];
  }

  // called from deployment cache manager
  private static InetAddress getByName(String host, InetAddress reqAddr)
      throws UnknownHostException {
    return InetAddress.getAllByName(host, reqAddr)[0];
  }

  /**
   * Given the name of a host, returns an array of its IP addresses,
   * based on the configured name service on the system.
   *
   * <p> The host name can either be a machine name, such as
   * "{@code java.sun.com}", or a textual representation of its IP
   * address. If a literal IP address is supplied, only the
   * validity of the address format is checked.
   *
   * <p> For {@code host} specified in <i>literal IPv6 address</i>,
   * either the form defined in RFC 2732 or the literal IPv6 address
   * format defined in RFC 2373 is accepted. A literal IPv6 address may
   * also be qualified by appending a scoped zone identifier or scope_id.
   * The syntax and usage of scope_ids is described
   * <a href="Inet6Address.html#scoped">here</a>.
   * <p> If the host is {@code null} then an {@code InetAddress}
   * representing an address of the loopback interface is returned.
   * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
   * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
   * section&nbsp;2.5.3. </p>
   *
   * <p> If there is a security manager and {@code host} is not
   * null and {@code host.length() } is not equal to zero, the
   * security manager's
   * {@code checkConnect} method is called
   * with the hostname and {@code -1}
   * as its arguments to see if the operation is allowed.
   *
   * @param host the name of the host, or {@code null}.
   * @return an array of all the IP addresses for a given host name.
   * @throws UnknownHostException if no IP address for the {@code host} could be found, or if a
   * scope_id was specified for a global IPv6 address.
   * @throws SecurityException if a security manager exists and its {@code checkConnect} method
   * doesn't allow the operation.
   * @see SecurityManager#checkConnect
   */
  public static InetAddress[] getAllByName(String host)
      throws UnknownHostException {
    return getAllByName(host, null);
  }

  private static InetAddress[] getAllByName(String host, InetAddress reqAddr)
      throws UnknownHostException {

    if (host == null || host.length() == 0) {
      InetAddress[] ret = new InetAddress[1];
      ret[0] = impl.loopbackAddress();
      return ret;
    }

    boolean ipv6Expected = false;
    if (host.charAt(0) == '[') {
      // This is supposed to be an IPv6 literal
      if (host.length() > 2 && host.charAt(host.length() - 1) == ']') {
        host = host.substring(1, host.length() - 1);
        ipv6Expected = true;
      } else {
        // This was supposed to be a IPv6 address, but it's not!
        throw new UnknownHostException(host + ": invalid IPv6 address");
      }
    }

    // if host is an IP address, we won't do further lookup
    if (Character.digit(host.charAt(0), 16) != -1
        || (host.charAt(0) == ':')) {
      byte[] addr = null;
      int numericZone = -1;
      String ifname = null;
      // see if it is IPv4 address
      addr = IPAddressUtil.textToNumericFormatV4(host);
      if (addr == null) {
        // This is supposed to be an IPv6 literal
        // Check if a numeric or string zone id is present
        int pos;
        if ((pos = host.indexOf("%")) != -1) {
          numericZone = checkNumericZone(host);
          if (numericZone == -1) { /* remainder of string must be an ifname */
            ifname = host.substring(pos + 1);
          }
        }
        if ((addr = IPAddressUtil.textToNumericFormatV6(host)) == null && host.contains(":")) {
          throw new UnknownHostException(host + ": invalid IPv6 address");
        }
      } else if (ipv6Expected) {
        // Means an IPv4 litteral between brackets!
        throw new UnknownHostException("[" + host + "]");
      }
      InetAddress[] ret = new InetAddress[1];
      if (addr != null) {
        if (addr.length == Inet4Address.INADDRSZ) {
          ret[0] = new Inet4Address(null, addr);
        } else {
          if (ifname != null) {
            ret[0] = new Inet6Address(null, addr, ifname);
          } else {
            ret[0] = new Inet6Address(null, addr, numericZone);
          }
        }
        return ret;
      }
    } else if (ipv6Expected) {
      // We were expecting an IPv6 Litteral, but got something else
      throw new UnknownHostException("[" + host + "]");
    }
    return getAllByName0(host, reqAddr, true);
  }

  /**
   * Returns the loopback address.
   * <p>
   * The InetAddress returned will represent the IPv4
   * loopback address, 127.0.0.1, or the IPv6 loopback
   * address, ::1. The IPv4 loopback address returned
   * is only one of many in the form 127.*.*.*
   *
   * @return the InetAddress loopback instance.
   * @since 1.7
   */
  public static InetAddress getLoopbackAddress() {
    return impl.loopbackAddress();
  }


  /**
   * check if the literal address string has %nn appended
   * returns -1 if not, or the numeric value otherwise.
   *
   * %nn may also be a string that represents the displayName of
   * a currently available NetworkInterface.
   */
  private static int checkNumericZone(String s) throws UnknownHostException {
    int percent = s.indexOf('%');
    int slen = s.length();
    int digit, zone = 0;
    if (percent == -1) {
      return -1;
    }
    for (int i = percent + 1; i < slen; i++) {
      char c = s.charAt(i);
      if (c == ']') {
        if (i == percent + 1) {
                    /* empty per-cent field */
          return -1;
        }
        break;
      }
      if ((digit = Character.digit(c, 10)) < 0) {
        return -1;
      }
      zone = (zone * 10) + digit;
    }
    return zone;
  }

  private static InetAddress[] getAllByName0(String host)
      throws UnknownHostException {
    return getAllByName0(host, true);
  }

  /**
   * package private so SocketPermission can call it
   */
  static InetAddress[] getAllByName0(String host, boolean check)
      throws UnknownHostException {
    return getAllByName0(host, null, check);
  }

  private static InetAddress[] getAllByName0(String host, InetAddress reqAddr, boolean check)
      throws UnknownHostException {

        /* If it gets here it is presumed to be a hostname */
        /* Cache.get can return: null, unknownAddress, or InetAddress[] */

        /* make sure the connection to the host is allowed, before we
         * give out a hostname
         */
    if (check) {
      SecurityManager security = System.getSecurityManager();
      if (security != null) {
        security.checkConnect(host, -1);
      }
    }

    InetAddress[] addresses = getCachedAddresses(host);

        /* If no entry in cache, then do the host lookup */
    if (addresses == null) {
      addresses = getAddressesFromNameService(host, reqAddr);
    }

    if (addresses == unknown_array) {
      throw new UnknownHostException(host);
    }

    return addresses.clone();
  }

  private static InetAddress[] getAddressesFromNameService(String host, InetAddress reqAddr)
      throws UnknownHostException {
    InetAddress[] addresses = null;
    boolean success = false;
    UnknownHostException ex = null;

    // Check whether the host is in the lookupTable.
    // 1) If the host isn't in the lookupTable when
    //    checkLookupTable() is called, checkLookupTable()
    //    would add the host in the lookupTable and
    //    return null. So we will do the lookup.
    // 2) If the host is in the lookupTable when
    //    checkLookupTable() is called, the current thread
    //    would be blocked until the host is removed
    //    from the lookupTable. Then this thread
    //    should try to look up the addressCache.
    //     i) if it found the addresses in the
    //        addressCache, checkLookupTable()  would
    //        return the addresses.
    //     ii) if it didn't find the addresses in the
    //         addressCache for any reason,
    //         it should add the host in the
    //         lookupTable and return null so the
    //         following code would do  a lookup itself.
    if ((addresses = checkLookupTable(host)) == null) {
      try {
        // This is the first thread which looks up the addresses
        // this host or the cache entry for this host has been
        // expired so this thread should do the lookup.
        for (NameService nameService : nameServices) {
          try {
                        /*
                         * Do not put the call to lookup() inside the
                         * constructor.  if you do you will still be
                         * allocating space when the lookup fails.
                         */

            addresses = nameService.lookupAllHostAddr(host);
            success = true;
            break;
          } catch (UnknownHostException uhe) {
            if (host.equalsIgnoreCase("localhost")) {
              InetAddress[] local = new InetAddress[]{impl.loopbackAddress()};
              addresses = local;
              success = true;
              break;
            } else {
              addresses = unknown_array;
              success = false;
              ex = uhe;
            }
          }
        }

        // More to do?
        if (reqAddr != null && addresses.length > 1 && !addresses[0].equals(reqAddr)) {
          // Find it?
          int i = 1;
          for (; i < addresses.length; i++) {
            if (addresses[i].equals(reqAddr)) {
              break;
            }
          }
          // Rotate
          if (i < addresses.length) {
            InetAddress tmp, tmp2 = reqAddr;
            for (int j = 0; j < i; j++) {
              tmp = addresses[j];
              addresses[j] = tmp2;
              tmp2 = tmp;
            }
            addresses[i] = tmp2;
          }
        }
        // Cache the address.
        cacheAddresses(host, addresses, success);

        if (!success && ex != null) {
          throw ex;
        }

      } finally {
        // Delete host from the lookupTable and notify
        // all threads waiting on the lookupTable monitor.
        updateLookupTable(host);
      }
    }

    return addresses;
  }


  private static InetAddress[] checkLookupTable(String host) {
    synchronized (lookupTable) {
      // If the host isn't in the lookupTable, add it in the
      // lookuptable and return null. The caller should do
      // the lookup.
      if (lookupTable.containsKey(host) == false) {
        lookupTable.put(host, null);
        return null;
      }

      // If the host is in the lookupTable, it means that another
      // thread is trying to look up the addresses of this host.
      // This thread should wait.
      while (lookupTable.containsKey(host)) {
        try {
          lookupTable.wait();
        } catch (InterruptedException e) {
        }
      }
    }

    // The other thread has finished looking up the addresses of
    // the host. This thread should retry to get the addresses
    // from the addressCache. If it doesn't get the addresses from
    // the cache, it will try to look up the addresses itself.
    InetAddress[] addresses = getCachedAddresses(host);
    if (addresses == null) {
      synchronized (lookupTable) {
        lookupTable.put(host, null);
        return null;
      }
    }

    return addresses;
  }

  private static void updateLookupTable(String host) {
    synchronized (lookupTable) {
      lookupTable.remove(host);
      lookupTable.notifyAll();
    }
  }

  /**
   * Returns an {@code InetAddress} object given the raw IP address .
   * The argument is in network byte order: the highest order
   * byte of the address is in {@code getAddress()[0]}.
   *
   * <p> This method doesn't block, i.e. no reverse name service lookup
   * is performed.
   *
   * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array
   * must be 16 bytes long
   *
   * @param addr the raw IP address in network byte order
   * @return an InetAddress object created from the raw IP address.
   * @throws UnknownHostException if IP address is of illegal length
   * @since 1.4
   */
  public static InetAddress getByAddress(byte[] addr)
      throws UnknownHostException {
    return getByAddress(null, addr);
  }

  private static InetAddress cachedLocalHost = null;
  private static long cacheTime = 0;
  private static final long maxCacheTime = 5000L;
  private static final Object cacheLock = new Object();

  /**
   * Returns the address of the local host. This is achieved by retrieving
   * the name of the host from the system, then resolving that name into
   * an {@code InetAddress}.
   *
   * <P>Note: The resolved address may be cached for a short period of time.
   * </P>
   *
   * <p>If there is a security manager, its
   * {@code checkConnect} method is called
   * with the local host name and {@code -1}
   * as its arguments to see if the operation is allowed.
   * If the operation is not allowed, an InetAddress representing
   * the loopback address is returned.
   *
   * @return the address of the local host.
   * @throws UnknownHostException if the local host name could not be resolved into an address.
   * @see SecurityManager#checkConnect
   * @see java.net.InetAddress#getByName(java.lang.String)
   */
  public static InetAddress getLocalHost() throws UnknownHostException {

    SecurityManager security = System.getSecurityManager();
    try {
      String local = impl.getLocalHostName();

      if (security != null) {
        security.checkConnect(local, -1);
      }

      if (local.equals("localhost")) {
        return impl.loopbackAddress();
      }

      InetAddress ret = null;
      synchronized (cacheLock) {
        long now = System.currentTimeMillis();
        if (cachedLocalHost != null) {
          if ((now - cacheTime) < maxCacheTime) // Less than 5s old?
          {
            ret = cachedLocalHost;
          } else {
            cachedLocalHost = null;
          }
        }

        // we are calling getAddressesFromNameService directly
        // to avoid getting localHost from cache
        if (ret == null) {
          InetAddress[] localAddrs;
          try {
            localAddrs =
                InetAddress.getAddressesFromNameService(local, null);
          } catch (UnknownHostException uhe) {
            // Rethrow with a more informative error message.
            UnknownHostException uhe2 =
                new UnknownHostException(local + ": " +
                    uhe.getMessage());
            uhe2.initCause(uhe);
            throw uhe2;
          }
          cachedLocalHost = localAddrs[0];
          cacheTime = now;
          ret = localAddrs[0];
        }
      }
      return ret;
    } catch (java.lang.SecurityException e) {
      return impl.loopbackAddress();
    }
  }

  /**
   * Perform class load-time initializations.
   */
  private static native void init();


  /*
   * Returns the InetAddress representing anyLocalAddress
   * (typically 0.0.0.0 or ::0)
   */
  static InetAddress anyLocalAddress() {
    return impl.anyLocalAddress();
  }

  /*
   * Load and instantiate an underlying impl class
   */
  static InetAddressImpl loadImpl(String implName) {
    Object impl = null;

        /*
         * Property "impl.prefix" will be prepended to the classname
         * of the implementation object we instantiate, to which we
         * delegate the real work (like native methods).  This
         * property can vary across implementations of the java.
         * classes.  The default is an empty String "".
         */
    String prefix = AccessController.doPrivileged(
        new GetPropertyAction("impl.prefix", ""));
    try {
      impl = Class.forName("java.net." + prefix + implName).newInstance();
    } catch (ClassNotFoundException e) {
      System.err.println("Class not found: java.net." + prefix +
          implName + ":\ncheck impl.prefix property " +
          "in your properties file.");
    } catch (InstantiationException e) {
      System.err.println("Could not instantiate: java.net." + prefix +
          implName + ":\ncheck impl.prefix property " +
          "in your properties file.");
    } catch (IllegalAccessException e) {
      System.err.println("Cannot access class: java.net." + prefix +
          implName + ":\ncheck impl.prefix property " +
          "in your properties file.");
    }

    if (impl == null) {
      try {
        impl = Class.forName(implName).newInstance();
      } catch (Exception e) {
        throw new Error("System property impl.prefix incorrect");
      }
    }

    return (InetAddressImpl) impl;
  }

  private void readObjectNoData(ObjectInputStream s) throws
      IOException, ClassNotFoundException {
    if (getClass().getClassLoader() != null) {
      throw new SecurityException("invalid address type");
    }
  }

  private static final long FIELDS_OFFSET;
  private static final sun.misc.Unsafe UNSAFE;

  static {
    try {
      sun.misc.Unsafe unsafe = sun.misc.Unsafe.getUnsafe();
      FIELDS_OFFSET = unsafe.objectFieldOffset(
          InetAddress.class.getDeclaredField("holder")
      );
      UNSAFE = unsafe;
    } catch (ReflectiveOperationException e) {
      throw new Error(e);
    }
  }

  private void readObject(ObjectInputStream s) throws
      IOException, ClassNotFoundException {
    if (getClass().getClassLoader() != null) {
      throw new SecurityException("invalid address type");
    }
    GetField gf = s.readFields();
    String host = (String) gf.get("hostName", null);
    int address = gf.get("address", 0);
    int family = gf.get("family", 0);
    InetAddressHolder h = new InetAddressHolder(host, address, family);
    UNSAFE.putObject(this, FIELDS_OFFSET, h);
  }

    /* needed because the serializable fields no longer exist */

  /**
   * @serialField hostName String
   * @serialField address int
   * @serialField family int
   */
  private static final ObjectStreamField[] serialPersistentFields = {
      new ObjectStreamField("hostName", String.class),
      new ObjectStreamField("address", int.class),
      new ObjectStreamField("family", int.class),
  };

  private void writeObject(ObjectOutputStream s) throws
      IOException {
    if (getClass().getClassLoader() != null) {
      throw new SecurityException("invalid address type");
    }
    PutField pf = s.putFields();
    pf.put("hostName", holder().getHostName());
    pf.put("address", holder().getAddress());
    pf.put("family", holder().getFamily());
    s.writeFields();
  }
}

/*
 * Simple factory to create the impl
 */
class InetAddressImplFactory {

  static InetAddressImpl create() {
    return InetAddress.loadImpl(isIPv6Supported() ?
        "Inet6AddressImpl" : "Inet4AddressImpl");
  }

  static native boolean isIPv6Supported();
}
